1. Field of the Invention
The present invention relates to an ink jet head which discharges ink through a nozzle hole onto a recording sheet by imparting a force to the contained ink within the ink jet head. The ink jet head of the present invention is suitably applicable to various image forming apparatuses including printers, facsimiles and copiers.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 7-125196 discloses a conventional ink jet head. FIG. 5A is a cross-sectional side view of the conventional ink jet head, and FIG. 5B is a cross-sectional view of the conventional ink jet head taken along a line Bxe2x80x94B of FIG. 5A.
As shown in FIG. 5A and FIG. 5B, the conventional ink jet head is constructed by joining together a first substrate 1, a second substrate 2 and a third substrate 3. These substrates 1, 2 and 3 are joined together so that a nozzle hole 4, an ink chamber 6, an orifice 7 and an ink cavity 8 are provided therein.
The first substrate 1 includes the ink chamber 6 and an oscillation plate 5 integrally formed with the first substrate 1. The oscillation plate 5 is located beneath the ink chamber 6. The second substrate 2 includes an individual counter electrode 9 which is disposed on the second substrate 2 and faces the oscillation plate 5 through an internal space or gap xe2x80x9cGxe2x80x9d between the oscillation plate 5 of the first substrate 1 and the counter electrode 9 of the second substrate 2. A lead of the counter electrode 9 on a mounted surface xe2x80x9cIxe2x80x9d and a common electrode (not shown) extending from the oscillation plate 5 on a mounted surface xe2x80x9cIIxe2x80x9d are electrically connected to a driver circuit 11. A driving voltage between the individual counter electrode 9 and the common electrode is supplied by the driver circuit 11.
Hereinafter, the first substrate 1 is referred to as the ink-chamber substrate 1, and the second substrate 2 is referred to as the counter-electrode substrate 2.
In the conventional ink jet head, when the driving voltage supply is turned on, an electrostatic force is created so as to downwardly pull the oscillation plate 5 toward the individual counter electrode 9. When the supplying of the driving voltage is turned off, the oscillation plate 5 is upwardly deflected so as to impart a force to and stress the ink within the ink chamber 6 such that the ink is discharged from the nozzle hole 4 onto a recording sheet 12.
As shown in FIG. 5A and FIG. 5B, in the structure of the above-mentioned ink jet head, the leads of the counter electrodes 9 are disposed on the mounted surface I, and the common electrode extending from the oscillation plate 5 is disposed on the mounted surface II. The mounted surface I of the leads of the counter electrodes 9 and the mounted surface II of the common electrode routed from the oscillation plate 5 have different heights. A mounting process for mounting the ink-chamber substrate 1 on the counter-electrode substrate 2, and a mounting process for mounting the third substrate 3 on the ink-chamber substrate 1 must be separately performed, and these processes are very complicated and expensive because the leads of the counter electrodes 9 and the common electrode are mounted on the mounted surfaces I and II with different heights.
Further, it is necessary to route the leads of the counter electrodes 9 to the connection points on the mounted surface xe2x80x9cIxe2x80x9d, as well as to route the common electrodes from the oscillation plates 5 to the connection points on the mounted surface xe2x80x9cIIxe2x80x9d, in order to establish both the electrical connection between the counter electrodes 9 and the driver circuit 11 and the electrical connection between the common electrodes and the driver circuit 11. This conventional ink jet head has connection points provided on the mounted surfaces xe2x80x9cIxe2x80x9d and xe2x80x9cIIxe2x80x9d with different heights, and requires the relatively-large ink-chamber substrate 1 and the relatively-large counter-electrode substrate 2. Accordingly, it is difficult for such a conventional ink jet head to achieve a high-density packaging of the counter electrodes and the oscillation plates in small-size substrates, as well as simple, inexpensive assembly processes.
Japanese Laid-Open Patent Application No. 5-169660 discloses another conventional ink jet head. FIG. 6 is a cross-sectional view of this conventional ink jet head.
As shown in FIG. 6, the conventional ink jet head includes a supporting board 21, a heater board 23 and a flexible wiring board 25. The heater board 23 is provided on the supporting board 21, and contains an energy-generating element which produces energy used to impart a force to and stress the ink within the conventional ink jet head in accordance with a print signal. When the energy is created by the energy-generating element of the heater board 23, the ink is discharged from a nozzle hole 22 onto a recording sheet.
In the conventional ink jet head of FIG. 6, the flexible wiring board 25 is provided on the supporting board 21, and the flexible wiring board 25 is electrically connected to the heater board 23 through a wire bonding or a tape automated bonding (TAB). A plurality of connection pads 24 are formed on the wiring board 25, and the wiring board 25 is connected through the connection pads 24 to a main part of a printing device. The main part of the printing device supplies the print signal to the wiring board 25 via the connection pads 24, and the wiring board 25 transfers the print signal to the heater board 23 via the bonded wire.
As shown in FIG. 6, in the structure of the above-mentioned conventional ink jet head, the flexible wiring board 25 must be bent at the end of the supporting board 21 so as to extend from the top surface of the supporting board 21 to the bottom surface thereof. The connection pads 24 are provided on the bottom surface of the wiring board 25, and the top surface of the wiring board 25 is connected to the heater board 23 by the bonded wire or the TAB.
The conventional ink jet head shown in FIG. 6 must be produced using the relatively-large supporting board 21, and the supporting board 21 must have an adequately large thickness for attaching the flexible wiring board 25 thereto. It is difficult that the conventional ink jet head of the above publication be provided with a smaller supporting board 21. Further, the conventional ink jet head of FIG. 6 requires the wire bonding or the TAB bonding, the mounting and bending of the flexible wiring board 25 and the soldering in order to provide the connection pads 24 on the bottom-side surface of the wiring board 25, and it is difficult to achieve simple, inexpensive assembly processes.
Further, Japanese Patent Application No. 9-148062, which is assigned to the owner of the present invention, discloses another conventional ink jet head. FIG. 7 is a cross-sectional view of the conventional ink jet head of the above-mentioned application.
As shown in FIG. 7, the conventional ink jet head includes a glass substrate 31 in which a via hole 32 is formed. A conductive material is plated in the via hole 32, and the via hole 32 serves as a conductive through hole in the glass substrate 31. The conventional ink jet head of FIG. 7 further includes an ink supply hole 37, an ink chamber 38, and a nozzle hole 39. An oscillation plate 33 under the ink chamber 38 is provided above the glass substrate 31, and a counter electrode 34 which faces the oscillation plate 33 through an internal space is provided in a recessed portion of the glass substrate 31.
In the conventional ink jet head of FIG. 7, a bump-plated conductor 35 is provided on the bottom of the glass substrate 31. The counter electrode 34 is electrically connected to the bump-plated conductor 35 by the via hole 32. A driving voltage between the counter electrode 34 and the oscillation plate 33 is externally supplied from the bump-plated conductor 35.
Similar to the ink jet head of FIG. 5A, in the conventional ink jet head of FIG. 7, when the driving voltage supply is turned on, an electrostatic force is created so as to downwardly pull the oscillation plate 33 toward the counter electrode 34 via the internal space. When the driving voltage supply is turned off, the oscillation plate 33 is upwardly deflected so as to impart a force to and stress the ink within the ink chamber 38, and the ink is discharged from the nozzle hole 39 onto a recording sheet.
In the structure of the conventional ink jet head of FIG. 7, it is difficult to form the via hole 32 in the glass substrate 31 with accurate dimensions because of the use of the glass substrate 31. It is also difficult to ensure an accurate depth of the gap between the counter electrode 34 and the oscillation plate 33. Accordingly, it is difficult for the conventional ink jet head of FIG. 7 to achieve a high-density packaging of the counter electrodes and the oscillation plates in small-size substrates as well as simple, inexpensive assembly processes.
In order to overcome the problems described above, preferred embodiments of the present invention provide an improved ink jet head which achieves a high-density packaging of the counter electrodes and the oscillation plates in small-size substrates as well as simple, inexpensive assembly processes.
According to one preferred embodiment of the present invention, an ink jet head discharges ink through a nozzle hole onto a recording sheet by stressing the ink within the ink jet head. The ink jet head includes a nozzle plate which has a nozzle hole, an ink-chamber substrate which is provided on a back of the nozzle plate and includes an integrally-formed oscillation plate and a pressure chamber, the pressure chamber containing ink and communicating with the nozzle hole, and the oscillation plate defining a bottom of the pressure chamber, a counter-electrode substrate which has an electrically isolated counter electrode, the counter electrode facing the oscillation plate via a gap between the oscillation plate and the counter electrode, a dielectric layer which is interposed between the ink-chamber substrate and the counter-electrode substrate, the dielectric layer being arranged to define the gap between the oscillation plate and the counter electrode, and a pad metal piece which is provided on a back of the counter electrode and is electrically connected to the counter electrode, and a driving voltage being externally supplied from the pad metal piece to the counter electrode so that the oscillation plate is actuated to stress the ink within the pressure chamber.
In another preferred embodiment of the ink jet head of the present invention, a dielectric layer preferably made of a thermal oxidation silicon dioxide is provided. The dielectric layer is interposed between the ink-chamber substrate and the counter-electrode substrate. The dielectric layer is arranged to define the gap between the oscillation plate and the counter electrode. The ink jet head having the dielectric layer arranged in this unique manner can be easily configured with low cost by using a photolithography and etching technique. Further, in this preferred embodiment of the ink jet head of the present invention, the pad metal piece is provided on the back of the counter electrode and is electrically connected to the counter electrode. Further, in this preferred embodiment of the ink jet head of the invention, the ink-chamber substrate is preferably made of a single-crystal silicon and the counter-electrode substrate is preferably made of either a single-crystal silicon or a metallic material. The ink jet head of preferred embodiments of the present invention having these elements arranged in the above manner is effective in achieving a high-density packaging of counter electrodes and oscillation plates in small-size substrates as well as simple, inexpensive assembly processes.